Variable pulley drive systems comprise a driveR and a driveN pulley, each of which is constructed of a pair of pulley flanges. At least one of the pair of pulley flanges is movable relative to the other. A belt, chain or the like connects the two pulleys. The driveR pulley is constructed so that the spacing between the flanges is changed by centrifuged force, hydraulic force, mechanical force or a combination thereof, which through the drive belt or chain causes corresponding changes in the spacing between the flanges of the driveN pulley.
Generally the flanges of the pulleys are linear, i.e., without steps and the like, so that an infinite number of speed changes can be provided throughout the operating range of the system. In some variable pulley drive systems, the pulley flanges are slotted, so that the flanges intermesh with one another during operation.